桂林水南洞1号石笋的沉积年代学研究

通过综合研究广西桂林盘龙洞1、2号、响水岩1号石笋,年龄分别为3万a,＞35万a,5．6万a;贵州荔波董歌洞3、4号、衙门洞1号石笋,年龄分别为16．3万～9．1万a,15．5万a,5．3万～0．7万a;都匀七星洞14、16号石笋,年龄分别为6．4万～1．9万,18．9万～14．9万a;湘西莲花洞1、5号石笋,年龄分别为6万～21a,8万～6万a。这些1．2～4 m高的巨型石笋,沉积旋回、纹(微)层、层面构造等特征,都很有典型性和代表性。根据石笋的宏观、微观沉积特征和系统测年,拟逐步取代测年精度不高的现行第四纪地质年表。笔者以水南洞1号石笋11个沉积旋回及其相关沉积特征为基础,采用TIMS-U系方法测年,精度高,作为桂林地区距今25万～15万a的地质年表。居于第四纪下限趋向＞250万a,建议以20万前后作为第四纪晚更新世与中更新世的断代分界,该分界处于石笋第3次沉积间断,期间形成厚达3 mm的风化壳,上下物质结构构造有显著差异。11个沉积旋回中,凡寒冷期沉积的碳和氧同位素都偏重,极值都是转冷的跃(突)变点,或沉积间断面。11次沉积间断时间长、短差别大,其中第3次、第9次分别为2万a、2千a。这些综合地质、气候信息在1号石笋纵剖面上呈协调显示,是重建古气候环境的可信依据。

Research on The Stalagmites Sedimentary Chronology——A Case Study on No. 1 Stalagmite of Shuinan Cave in Guilin, China

The stalagmite P1,P2 of Panlong cave and stalagmite X1 of Xiangshui cave in Guilin(which their ages are 30 ka BP,over 350 ka BP and 56ka BP,respectively),the stalagmite D3,D4 of Dongge cave and stalagmite Y1 of Yaman cave in Libo(which their ages are from 64 ka BP to 19ka BP,over 155 ka BP and from 53ka BP from 7.3 ka BP,respectively),the stalagmite Q14,Q16 of Qixing cave in Duyun(which their ages are from 64 ka BP to 19ka BP,over 155 ka BP and from 53ka BP from 7.3 ka BP, respectively),Guizhou,and the stalagmiteLL1,LL5 of Linhua cave in longshan(which their ages are from 60 ka BP to 21a BP,and from 80ka BP from 6 ka BP,respectively),Hunan,have been studied and integrated for many years.The characteristics of depositional cycles,micro-lamina and bedding plane structure in large stalagmites with height from 150cm to 400cm have obviously typicalness and representativeness.The dating precision low of the present Quaternary chronological scale will progressively be replaced on the basis of macroscopic and microscopic deposit characteristics and systematic dating ages from stalagmites in caves.Author has established the chronological scale from 150ka to 250ka BP in Guilin areas on the basis of 11 depositional cycles from N0.1 stalagmite of Shuinan cave and relative deposit characteristics and using of high precisional TIMS-U series dating.We suggest that the division boundary of chronology between the late Pleistocene and the middle Pleistocene is ca.200ka BP as the bottom boundary of Quaternary chronology is over 2500 ka.The boundary of chronology locates at third depositional hiatuse from N0.1 stalagmite of Shuinan cave,which formed 3mm weathering crust and has a markedness difference at the upper and lower material texture and structure.The carbon and oxygen isotope from the cold deposit stalagmites in 11 depositional cycles are a heavy or positive trend and the maximum value point is an abrupt point of transferring cold or depositional hiatus surface.The duration of 11 depositional hiatuses has obvious difference,in which the duration of third and ninth depositional hiatuses is 20ka,2ka,respectively.The information of the synthetically geology and climate is a good correlation and possible evident of reconstructing paleoclimate and environment.